Nucleotide sequence and phylogeny of SHV-2 beta-lactamase.
We determined the nucleotide sequence of the blaSHV-2(pBP60-1) gene from Klebsiella ozaenae which confers resistance to broad-spectrum cephalosporins. The structural gene encodes a polypeptide product of 286 amino acids, and the estimated molecular weight of the mature protein is 28,900. Amino acid sequence comparison of the SHV-2pBP60-1 enzyme with all known class A beta-lactamases and homology studies showed that the residues were highly conserved. Furthermore, SHV-2pBP60-1 was clearly related to SHV-1, LEN-1, and OHIO-1. The SHV-2pBP60-1 enzyme differed from SHV-1 isolated from Klebsiella pneumoniae by seven amino acid substitutions. One of these substitutions, the Gly----Ser substitution at position 234, is probably a key region for the novel activity of cefotaxime hydrolysis. A phylogenetic tree was constructed by using all class A beta-lactamases of known sequences by a progressive alignment method. The data suggested that the beta-lactamases of gram-positive Streptomyces, Staphylococcus, and Bacillus species appeared early in evolution, followed by the PSE and CARB enzymes of Pseudomonas species and, more recently, by the SHV-type and TEM-type enzymes found in enteric bacteria. Larger evolutionary distances separated clusters of the gram-positive beta-lactamases than separated clusters of the gram-negative enzymes. Results of this phylogenetic study suggested that extended-spectrum enzymes are recent derivatives that are selected by the use of new cephalosporins.
Huletsky
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Département de Microbiologie, Faculté de Médecine, Université Laval, Quebec, Canada.
Couture
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Levesque
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RC
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D007709:Klebsiella / Q000201:enzymology / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D012689:Sequence Homology, Nucleic Acid; D001618:beta-Lactamases / Q000235:genetics*
D001426:Bacterial Proteins; C062760:beta-lactamase SHV-2; D001618:beta-Lactamases